1. Field of the Invention
The present invention is directed to a process of removing residue from a precision surface. More specifically, the present invention is directed to the removal of residue material from a precision surface which has been subjected to an etching process, such as reactive ion etching (RIE), by exposing the precision surface to a composition which comprises liquid or supercritical carbon dioxide and a fluoride generating species.
2. Background of the Prior Art
Semiconductor manufacture involves etching of surfaces of metals and glass-like insulators protected by a photoresist surface in order to define electrical circuitry on the semiconductor device. The photoresist material is thereupon stripped from the surface in an oxygen plasma. This processing leaves residues that must be removed by chemicals and/or solvents in order to achieve high yield.
An example of the above procedure is the etching of aluminum to define wiring on a semiconductor wafer. Despite cleaning and rinsing of the semiconductor wafer, unwanted residue remains on the top and the side walls of the metal lines. This unwanted residue includes several elements including carbon, hydrogen, silicon, aluminum, fluorine, chlorine and oxygen. This reaction ion etching (RIE) residue is conductive enough to cause shorts between metal lines. In addition, RIE residue may also cause adhesion problems between the metal lines and an overlaying insulator. The RIE residue on metal lines may additionally cause corrosion of the semiconductor sample. Furthermore, the RIE residue on polysilicon lines or oxide vias also cause yield loss problems.
These considerations have resulted in a considerable degree of activity in developing a chemically safe and easy method of removing RIE residue from a semiconductor sample. To this end U.S. Pat. No. 5,976,264 has proposed the removal of fluorine or fluorine residue by liquid carbon dioxide. A similar method is proposed in U.S. Pat. No. 5,908,510. This method includes the alternative utilization of a cryogenic aerosol. However, these methods have been found to swell polymeric constituents present on the semiconductor device. U.S. Pat. No. 5,738,082 also suggests the cleaning of silicon wafers with liquid carbon dioxide. The '082 patent suggests the inclusion of a surfactant. This patent, however, does not address the removal of RIE residue.
To sum up the state of the art, the use of supercritical fluids have been advanced for removing RIE residues but this proposal has met with only limited success. This is so insofar as polymeric residues result from a complex structure of carbon to fluorine and carbon to oxygen bonds. This complex polymeric structure bears a strong resemblance to polytetrafluoroethylene. Although Kirby et al., Chemical Rev., 99, 565-602 (1999) discloses that polytetrafluoroethylene is somewhat soluble in liquid carbon dioxide, the mere utilization of liquid or supercritical carbon dioxide has been found to be insufficient to remove RIE residue. Thus, it is apparent to those skilled in the art that more than liquid or supercritical carbon dioxide alone is required to completely remove RIE residue from precision surfaces.